Alkyl phosphinates or bis(alkyl)phosphinates can be prepared by the reaction of an olefin with an alkali metal salt of hypophosphorous acid. For example, the reaction of a 1:1 mole ratio of an alpha-olefin with sodium hypophosphite yields the corresponding sodium alkyl phosphinate when initiated photochemically in the presence of a photoinitiator, or thermally in the presence of an introduced chemical source of free radicals such as a peroxide. The reaction may be summarized as follows: ##STR1##
Alkyl phosphinate I can be converted into the corresponding phosphonate (RCH.sub.2 CH.sub.2 P(O)(ONa).sub.2) by exposure to an oxidizing agent. Both the alkyl phosphonates and alkyl phosphinates can function as anionic surfactants, and can act to enhance the wetting power of aqueous media.
Although the alkali metal phosphinates may be useful as surfactants additives for household and industrial detergents, this potential has not been realized due to the barriers encountered to efficient, commercially-viable syntheses of this class of compounds. For example, numerous yield-reducing side reactions, including telomerization, double bond polymerization, abstraction of alkylic hydrogen atoms and hypophosphorous acid oxidation can occur. In Tenside Detergents, Vol. 18, 190 (1981), C. H. Agustin extensively examined reaction variables with respect to the synthesis of sodium octylphosphinate from 1-octene and sodium hypophosphite monohydrate in water/ethanol, initiated by t-butyl perbenzoate. He achieved product yields of greater than 90% by dividing the unstable initiator into two equal portions. One of them was introduced into the reaction vessel with the hypophosphite, while the second one was dissolved in the 1-octene and added gradually to the refluxing solvent system, which presumably contained preformed hypophosphite radicals. Agustin concluded that a reflux time of 45 hours was essential to obtain a product with satisfactory wetting power which was calculated to be 96% sodium octyl phosphinate. Reaction times of 12.3-15.5 hours yielded a product of low wetting power which was not further analyzed.
Attempts to prepare organic phosphinates and phosphonate esters by photochemical initiation have also resulted in low yields. A. R. Stiles et al. (U.S. Pat. No. 2,724,718) disclosed that a 54.5% yield of dibutyl octane-1-phosphonate was obtained by irradiating a mixture of 1-octene, dibutylphosphite and acetone with ultraviolet light for 7 hours at 25.degree. C.
Due to increasing labor and energy costs, a need exists for a synthesis of alkyl phosphinates which will produce equivalent or higher yields while permitting substantially decreased reaction times.